Abstract: A power transmission apparatus for four-wheel drive vehicle which uses a hydraulic pump to absorb a rotational speed difference caused between front and rear wheels or left side and right side wheels to thereby materialize the four-wheel drive state and which is provided at a fixed housing with a variable throttle for adjusting oil pressure at the hydraulic pump. The variable throttle is adjustable of a degree of its opening by brake oil pressure generated by the braking action during the drive operation of an electromagnetic actuator or oil pressure introduced into a power cylinder disposed in a steering mechanism. Also, outside the fixed housing are provided fins for dissipating the heat content of operating oil at the hydraulic pump. Furthermore, on the slidable contact surface of a casing of the hydraulic pump with the fixed housing is provided sealing means for preventing the operating oil in the hydraulic pump from leaking therefrom.